Basement membranes are the principal extracellular matrices for most tissues, providing physical support, molecular filtering, and cell regulatory functions. Basement membranes consist of a unique set of proteins, and their composition and function are different in various tissues. Recombinant DNA techniques have been used to determine the structure and functions of basement membranes proteins. New components of basement membranes have been identified and studies of their tissue specificity and function have been in progress. Approaches of synthetic peptides and expression of recombinant proteins have been applied to understand the mechanisms of the molecular assembly of basement membrane molecules. DNA elements which regulate genes for basement membrane proteins have been localized in the promoter and enhancer regions and examined for their gene specificity. Nuclear factors which bind to some of these DNA elements have been cloned and sequenced. The protein factors have been expressed in bacteria and mammalian cells to study their cell type specificity and their function.